A Modified Arbuzov-Michalis Reaction for Selective Alkylation of Nucleophiles.

The alkylation of nucleophiles is among the most fundamental and well-developed transformations in chemistry. However, to achieve selective alkylation of complex substrates remains a nontrivial task. We report herein a general and selective alkylation method without using strong acids, bases, or metals. In this method, the readily available phosphinites/phosphites, in combination with ethyl acrylate, function as effective alkylating agents. Various nucleophilic groups, including alcohols, phenols, carboxylic acids, imides, and thiols can be alkylated. This method can be applied in the late-stage alkylation of natural products and pharmaceutical agents, achieving chemo- and site-selective modification of complex substrates. Experimental studies indicate the relative reactivity of a nucleophile depends on its acidity and its steric environment. Mechanistic studies suggest the reaction pathway resembles that of the Arbuzov-Michalis reaction.

Generation of Glycosyl Radicals from Glycosyl Sulfoxides and Its Use in the Synthesis of C-linked Glycoconjugates.

We here report glycosyl sulfoxides appended with an aryl iodide moiety as readily available, air and moisture stable precursors to glycosyl radicals. These glycosyl sulfoxides could be converted to glycosyl radicals by way of a rapid and efficient intramolecular radical substitution event. The use of this type of precursors enabled the synthesis of various complex C-linked glycoconjugates under mild conditions. This reaction could be performed in aqueous media and is amenable to the synthesis of glycopeptidomimetics and carbohydrate-DNA conjugates.

A Radical Approach to Making Unnatural Amino Acids: Conversion of C-S Bonds in Cysteine Derivatives into C-C Bonds.

Here we report a general approach to make unnatural amino acids from readily available cysteine derivatives. This method capitalizes on an intramolecular radical substitution process that generates alkyl radicals through C-S cleavage. The resulting alkyl radicals partook in diverse C-C bond forming events. These reactions proceed under mild, photocatalytic conditions at room temperature, and can be performed open to air. The utility of these transformations is further demonstrated in the straightforward synthesis of various unnatural amino acids and peptides that are difficult to access previously.

Site-Selective O-Arylation of Glycosides.

Direct and site-selective O-arylation of carbohydrates has been a challenge in synthesis. Herein we report a method based on copper-catalyzed O-arylation to address this challenge. Proper choice of the ancillary ligand on copper is critical for the efficiency and site selectivity of this transformation. This method features mild conditions, tolerates various functional groups, and demonstrates broad substrate scope.

"Half-sandwich" Schiff-base Ir(III) complexes as anticancer agents.

A series of "half-sandwich" Schiff-base Ir(III) complexes were synthesized and investigated for their in vitro activities against the leukemia K562 cell line. These compounds demonstrated antiproliferative activities against K562 cells with IC50 values of 0.26-4.77 µM. In particular, compound 10c showed cytotoxicity against five cancer cell lines/sublines and stronger activities than cisplatin in K562, K562/A02, MCF-7, MCF-7/ADM, and A549 cells. Mechanism studies illustrated that compound 10c increased the level of reactive oxygen species and induced apoptosis of K562 cells. This compound effectively decreased the mitochondrial membrane potential and the protein level of Bcl-2. It also increased the protein levels of Bax, caspase-3, and caspase-9, and led to release of cytochrome c in K562 cells, indicating that the apoptosis induced by compound 10c was mediated by the intrinsic mitochondria apoptosis pathway.